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8282144: RandomSupport.convertSeedBytesToLongs sign extension overwri…
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…tes previous bytes

Reviewed-by: bpb
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JimLaskey committed Mar 8, 2022
1 parent 65ca0a5 commit 5fab27e
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Original file line number Diff line number Diff line change
Expand Up @@ -265,7 +265,7 @@ public static long[] convertSeedBytesToLongs(byte[] seed, int n, int z) {
final int m = Math.min(seed.length, n << 3);
// Distribute seed bytes into the words to be formed.
for (int j = 0; j < m; j++) {
result[j>>3] = (result[j>>3] << 8) | seed[j];
result[j>>3] = (result[j>>3] << 8) | (seed[j] & 0xFF);
}
// If there aren't enough seed bytes for all the words we need,
// use a SplitMix-style PRNG to fill in the rest.
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71 changes: 71 additions & 0 deletions test/jdk/java/util/Random/T8282144.java
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@@ -0,0 +1,71 @@
/*
* Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/

import java.util.random.*;
import jdk.internal.util.random.RandomSupport;

/**
* @test
* @summary RandomSupport.convertSeedBytesToLongs sign extension overwrites previous bytes.
* @bug 8282144
* @modules java.base/jdk.internal.util.random
* @run main T8282144
* @key randomness
*/


public class T8282144 {
public static void main(String[] args) {
RandomGenerator rng = RandomGeneratorFactory.of("L64X128MixRandom").create(42);

for (int i = 1; i < 8; i++) {
byte[] seed = new byte[i];

for (int j = 0; j < 10; j++) {
rng.nextBytes(seed);

long[] existing = RandomSupport.convertSeedBytesToLongs(seed, 1, 1);
long[] testing = convertSeedBytesToLongsFixed(seed, 1, 1);

for (int k = 0; k < existing.length; k++) {
if (existing[k] != testing[k]) {
throw new RuntimeException("convertSeedBytesToLongs incorrect");
}
}
}
}
}


public static long[] convertSeedBytesToLongsFixed(byte[] seed, int n, int z) {
final long[] result = new long[n];
final int m = Math.min(seed.length, n << 3);

// Distribute seed bytes into the words to be formed.
for (int j = 0; j < m; j++) {
result[j >> 3] = (result[j >> 3] << 8) | (seed[j] & 0xff);
}

return result;
}
}

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